The effectiveness of radiotherapy would be improved if radiosensitizing drugs were used which acted differentially in sensitizing cancer cells more than normal tissues. Recent studies of lucanthone (Miracil D), 1-diethylamino-ethylamino-4-methyl-10-thioxanthenone, a relatively non-toxic drug widely used in the treatment of schistosomiasis, indicate that it radiosensitizes by inhibiting repair of radiation damage, localizes in certain neoplastic tissues more than in adjacent skin and muscle, and causes a substantial radiosensitization of mouse tumors with little or no sensitization of adjacent normal tissues. In addition, limited clinical results indicate that lucanthone halved the 50% regression time following radiotherapy for the two tumor types tested. The objectives of this project are: (1) to determine in preclinical studies the optimum timing and optimum radiation dose rate for effective use of the drug, lucanthone, in radiation therapy and (2) to determine in mice the extent of any possible radiosensitization with lucanthone of several important dose limiting normal tissues. The results will help to define more nearly optimum treatment parameters and favorable treatment situations for use of this promising radiosensitizing drug in radiation therapy. BIBLIOGRAPHIC REFERENCES: Darrell Q. Brown, John Pittock, Lawrence Coia, Andrew Milligan and Lenn Chalfin. Radiosensitization of C3H Mammary Tumors Using Lucanthone and a Medium Dose Rate. Radiation Research 67:637 (1976). S. S. Agarwal, D. Q. Brown, E. J. Katz and L. A. Loeb. DNA Repair in Human Lymphocytes. In Genetics of Human Cancer, ed. by John J. Mulvihill, et al., Raven Press, New York, N.Y., 1977 pp. 365-368.